1. Field of the Invention
The present invention relates generally to an apparatus used in the construction of precast, moment-resisting frames of buildings. More particularly the invention concerns an apparatus for use in positioning a plurality of mild steel bars within a precast, moment resisting frame made up of columns and beams and for grouting the interfaces between the beams and columns.
2. Discussion of the Prior Art
In recent years great strides have been made in the design of high rise buildings that resist lateral forces as well as vertical or gravity forces. Lateral or horizontal forces are normally imposed on a building or structure by either wind forces or seismic forces applied to the building. Of particular concern in earthquake-prone areas are seismic forces, and great strides have been made in these areas in the design of seismic-resistant structures. However, experience has shown that even relatively new seismic-resistant, steel-frame buildings have serious short-comings. For example, building codes are typically written with personal safety in mind and generally require that certain structural members bend to absorb the force of a serious quake and, in this way, spare the occupants of the building. However, following the earthquake, buildings constructed to these codes, while preserving human life may, nevertheless require major repairs, and, in some cases the entire building must be demolished because of the structural damage suffered.
One of the most successful prior art moment resisting frame designs is the design developed by the assignee of the present invention. This novel design concerns precast moment resisting frames made up of columns and beams that are tied together in the horizontal direction by high-strength cables. These cables are entrained through a passageway located in the center of the beam so as to pass through the columns at the same elevation as the beam. In these structures, after the beam and column elements are erected, the cables are entrained through the passageways and stretched or tensioned. The stretched cables are clamped at the face of the columns resulting in the horizontal force that securely ties the columns and beams together. In some moment frames the horizontal ducts carried within the beams may contain as many as twenty, 0.6-inch-diameter, high-strength cables with a post tensioned force of on the order of 35,000 pounds each. Accordingly, the resulting force acting on the column from the two perpendicular forces transferred to the column may well exceed four hundred tons.
In addition to the high strength cables, the columns and beams of this novel frame design are connected together with reinforcing steel that absorbs energy during lateral movement of the frame. More particularly, at every location where a beam meets a column, steel bars, which are strategically located above and below the central cable, help secure the joint. Made of stretchy or xe2x80x9cmildxe2x80x9d steel, the bars uniquely serve to effectively dampen the earthquake""s effects.
In an earthquake that causes the building to shake and the vertical columns to sway, the central steel cable of the aforementioned prior art designs will stretch safely and rebound slightly without permitting the beam-to-column joints to shift out of alignment. The mild-steel bars or rods, because of their placement above and below the central cable at each joint, take the brunt of the sideways forces, stretching and retracting much like very large shock absorbers. When the earthquake ends, the frame snaps back to its original shape without major structural damage having occurred.
Significant problem recognized in the prior art construction concern the positioning of the mild steel bars during construction as well as the accomplishment of the grouting step at the interfaces between the beams and the columns. The thrust of the present invention is to provide a novel method and apparatus for accomplishing both of these troublesome operations, namely the positioning of the mild steel bars within the structure and the grouting of the interfaces between the beams and the columns.
It is an object of the present invention to provide a novel method and apparatus for positioning mild steel reinforcing bars within a precast moment resisting frame of a building. More particularly it is an object of the invention to provide a uniquely configured, hand-receiving access component that can be installed within the concrete beams that make up the building frame so as to permit convenient access to the reinforcing bars that are slidably carried within bar receiving passageways formed within the concrete beams.
Another object of the invention is to provide a novel means for grouting the interfaces between the concrete beams and the concrete columns that make up the building frame. In this regard, it is a specific object of the invention to provide a bladder-receiving component that can be installed within the concrete beams that make up the building frame in a manner permit an expandable bladder to be conveniently positioned within the cable receiving passageways formed in the beam. When in position within a cable-receiving passageway, the expandable bladder spans the interface between the beam and the column and effectively prevents grout from entering the cable passageway during the grouting step.
Another object of the invention is to provide a grouting means of the character described in the preceding paragraph in which the expandable bladder, when in position within the cable receiving passageway, can be expanded into sealable engagement with the walls of the cable receiving passageway during the grouting step and then can be deflated for easy removal from the structure after the grouting step via the bladder receiving component.
Another object of the invention is to provide a method of the aforementioned character in which both the hand receiving components and the bladder receiving components can be cast into the concrete beams on the ground so that the steel bars can be introduced into the bar passageways formed in the concrete beams prior to the beams being raised into the correct elevated position relative to the vertical columns which make up the structure. With the beams in the elevated position the steel bars can be accessed through the hand receiving components and moved into a final position wherein the rods span the adjacent vertical column and extend into the abutting beam.
These and other objects of the invention will become apparent from the description that follows.